For a fuel cell separator, there have been attempted a cutting from a graphite material, a molding of an electroconductive thermosetting resin composition, a molding of an electroconductive thermoplastic resin composition, and a metal product. However, the cutting from a graphite material has a problem of a high cost and low mass productivity; the molding of an electroconductive thermosetting resin composition has problems of a low mass productivity because of a long molding cycle, need for troublesome post-processing, such as removing flashes after molding, and then a lowered performance because of the elution of unreacted substances. Also, it is difficult for the molding of the conventional electroconductive thermoplastic resin composition to achieve compatibility between electric conductivity and fluidity. The metal product has problems of a deteriorated electrolyte membrane due to the elution of the metallic ions, and catalyst poisoning. To solve these problems, gold plating on the surface is attempted, but not practical because of a high cost.
On the other hand, a liquid-crystalline polymer, which is capable of forming an anisotropic molten phase, is known as a material which exhibits excellent dimensional accuracy, damping property, and fluidity as compared to other thermoplastics and rarely forms flash during molding. So far, taking the above advantages into consideration, the composition of a liquid crystalline polymer reinforced with a glass fiber has been widely employed as electronic parts. In recent years, the liquid crystalline polymer has been supplemented with an electroconductive filler to impart an electrical conductivity, in addition to the excellent fluidity.
For example, JP-A 62-131067 attempted to add an electroconductive carbon black to a liquid crystalline polymer in order to improve the electric conductivity. This method allows for improvement of the electric conductivity, but needs an increased amount of filled carbon black to have a volume resistivity of not more than 5×10−2 Ω·cm. It is therefore too viscous and has difficulty in molding because the structure of such an electroconductive carbon black is developed. JP-A 6-207083 has then attempted to add graphite as an electroconductive filler to improve the antistatic property. It is, however, difficult with this method to impart a necessary electric conductivity to a fuel cell separator. Moreover, JP-A 63-146959, JP-A 4-311758, JP-A 6-93173, JP-A 6-172619, JP-A 6-271748, and JP-A 7-18162 have attempted to add a specified graphite and/or a pitch-based carbon fiber to enhance slidability. This method allows recognizable improvement of the slidability, but it is also difficult even with this method to impart a necessary electric conductivity to a fuel cell separator.
Further, JP-A 11-354136 has attempted to use expanded graphite having a particle size of not less than a specific value for the separator in order to improve the electric conductivity, gas permeability and the like. This method allows recognizable improvement of the electric conductivity, but it is difficult with this method to blend the expanded graphite with a thermoplastic resin because of a low bulk specific gravity of expanded graphite.
Furthermore, JP-A2001-126744 has attempted to use a coarse particle graphite having a specified particle size for the separator in order to improve the electric conductivity, the mechanical strength, the dimensional accuracy and the like. This method does not necessarily improve the electric conductivity and the mechanical strength depending on kneading conditions, instead raises problems of deterioration in fluidity, generation of gas due to degradation, a decrease in the mechanical strength, deterioration in moldability and the like due to unsatisfied kneading,    Patent Document 1: JP-A 62-131067    Patent Document 2: JP-A 6-207083    Patent Document 3: JP-A 63-146959    Patent Document 4: JP-A 4-311758    Patent Document 5: JP-A 6-93173    Patent Document 6: JP-A 6-172619    Patent Document 7: JP-A 6-271748    Patent Document 8: JP-A 7-18162    Patent Document 9: JP-A 11-354136    Patent Document 10: JP-A 2001-126744